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Abstrakt
Context.We present results from non linear MHD dynamo experiments with a threedimensional steady and smooth flow that drives fast dynamo action in the kinematic regime. In the saturation regime, the system yields strong magnetic fields, which undergo transitions between an energyequipartition and a turbulent state. The generation and evolution of such strong magnetic fields is relevant for the understanding of dynamo action that occurs in stars and other astrophysical objects.
Aims.We study the mode of operation of this dynamo, in the linear and nonlinear saturation regimes. We also consider the effect of varying the magnetic and fluid Reymolds number on the nonlinear behaviour of the system.
Methods.We perform threedimensional nonlinear MHD simulations and visualization using a high resolution numerical scheme.
Results.We find that this dynamo has a high growth rate in the linear regime, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain timeindependent during the simulation but exhibits a much more intricate behaviour than previously thought. There are periods in time where the solution is smooth and close to energyequipartition and others where it becomes turbulent. Similarities and differences in the way the magnetic field is amplified and sustained for experiments with varying Reynolds numbers are discussed.
Conclusions.Strong magnetic fields, in near equipartition, can be generated also by a nonturbulent dynamo. A striking result is that the saturation state of this dynamo reveals interesting transitions between turbulent and laminar states.
Aims.We study the mode of operation of this dynamo, in the linear and nonlinear saturation regimes. We also consider the effect of varying the magnetic and fluid Reymolds number on the nonlinear behaviour of the system.
Methods.We perform threedimensional nonlinear MHD simulations and visualization using a high resolution numerical scheme.
Results.We find that this dynamo has a high growth rate in the linear regime, and that it can saturate at a level significantly higher than intermittent turbulent dynamos, namely at energy equipartition, for high values of the magnetic and fluid Reynolds numbers. The equipartition solution however does not remain timeindependent during the simulation but exhibits a much more intricate behaviour than previously thought. There are periods in time where the solution is smooth and close to energyequipartition and others where it becomes turbulent. Similarities and differences in the way the magnetic field is amplified and sustained for experiments with varying Reynolds numbers are discussed.
Conclusions.Strong magnetic fields, in near equipartition, can be generated also by a nonturbulent dynamo. A striking result is that the saturation state of this dynamo reveals interesting transitions between turbulent and laminar states.
Originalsprog  Engelsk 

Tidsskrift  Astronomy & Astrophysics 
Vol/bind  472 
Udgave nummer  3 
Sider (fratil)  715726 
ISSN  00046361 
DOI  
Status  Udgivet  2007 
Udgivet eksternt  Ja 
Bibliografisk note
Paper id:: 10.1051/00046361:20065087Fingeraftryk
Dyk ned i forskningsemnerne om 'Nonlinear MHD dynamo operating at equipartition'. Sammen danner de et unikt fingeraftryk.Relaterede Projekter
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MAGSTAR: Forskningstema 1: Astrofysisk magnetisme
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Projekter: Projekt › Forskning